1. Field of the Invention
The present invention relates to an integrated circuit for controlling battery cell and a vehicle power supply system that uses the integrated circuit.
2. Description of Related Art
There are vehicle power supply systems known in the related art that include an inverter connected to a rotating electrical machine and a multi-series battery control system.
A drive system for a vehicle rotating electrical machine is provided with a secondary battery for supplying DC power and an inverter device that converts the DC power supplied from the secondary battery to three-phase AC power. The three-phase AC power is supplied to the rotating electrical machine installed in the vehicle. A three-phase AC rotating electrical machine generally includes a function as an electric motor and a function as a power generator. If a three-phase AC rotating electrical machine is operated as a power generator such as in regenerative braking operation, the three-phase AC power generated by the rotating electrical machine is converted to DC power by the inverter device. The DC power is supplied to the secondary battery. The generated power is stored in the secondary battery.
A lithium battery module is suitable for a secondary battery because a large amount of power can be stored in a small-sized module. A lithium battery module includes numerous serially connected lithium battery cells. It is desirable to individually detect the state of charge of each of the lithium battery cells and to manage it so as not to be in an over-charged state. It is to be noted that the state of charge will be abbreviated as the SOC below. It is desirable to manage charge/discharge of each of the lithium battery cells, for instance, so as not to be in an over-discharged state: Keeping an over-discharged state may cause excessive heat.
There is a vehicle power supply system including a lithium battery disclosed in, for instance, Japanese Laid Open Patent Publication No. 2005-318751.
The terminal voltage of each of the lithium battery cells is detected so as to prevent each of the lithium battery cells from being over-charged. Thus, each of the lithium battery cells is monitored. Since a vehicle power supply may be used for long periods under conditions with constant vibrations and severe temperature changes, it is desired to pay sufficient attention to reliability.